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,1 New. 21, 1950 G. T. BAKER 2,530,802

TELEPHONE SYSTEM EMPLOYING FINDER SWITCHES FOR CONNECTING CALLING LINESTO NUMERICAL SWITCHES Original Filed Nov. 11, 1944 18 Sheets-Sheet 1FIG] INVENTOR. GEO RGE THOMAS BAKER ATTORNEY Nov. 21, 1950 G. 'r. BAKER2,530,302

I TELEPHONE SYSTEM EMPLOYING FINDER SWITCHES FOR CONNECTING CALLINGLINES T0 NUMERICAL SWITCHES Original Filed Nov. 11, 1944 18 Sheets-Sheet2 I I 5 06 I ATTORNEY Nov. 21, 1950 G T BAKER 2,530,802

TELEPHONE SYSTEM ENPLOYING FINDER SWITCHES FOR CONNECTING CALLING LINESTO NUMERICAL SWITCHES Original Filed Nov. 11, 1944 18 Sheets-Sheet 3 s O--P u; LF FS CE is v v TRI E THI I I [2 RD I r Q I INVENTOR. GEORGETHOMAS BAKER ATTORNEY Nov. 21, 1950 G. T. BAKER 2,530,802

TELEPHONE SYSTEM EMPLOYING FINDER SWITCHES FOR CONNECTING CALLING LINESTO NUMERICAL SWITCHES Original Filed Nov. 11, 1944 18 Sheets-Sheet 4FIG. 4

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JNVENTOR. GEORGE THOMAS BAKER ATTORNEY Nov. 21, 1950 G. T. BAKER2,530,802

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ENG l T'T- RN! PR2 E I'll ENR3 ma ERLIT I EIC8 E82 INVENTOR. GEORGETHOMAS BAKER ATTORNEY l atentecl Nov. 21, 1950 UNITED STATES ATENTOFFICE TELEPHONE SYSTEM EMPLOYING' SiiITGHES FUR CONNECTING CALLINGLINES TO NUMERICAL SWETCHES George Thomas Baker, Liverpool, England, as-

ignor to Automatic Electric Laboratories, Inc.-, Qhicago, ill, acorporation of Delaware September 16, 1M4

iii Claims.

The present invention relates to telephone systems, and as regards mostof its'ieatures is particularly applicable to rural telephone networksinvolving a main exchange through which all calls incoming to oroutgoing from the network are handled, and a number of outlying ruralexchanges which serve in either a tandem or terminal capacity.

In such networks the various outlying exchanges are usually so small asto render a 24- hour manual service extremely expensive and inefficient,while with regard to possible automatic working, the subscribers lineconditions are often well below the standard required for satisfactoryimpulsing to automatic exchange equipment. A solution already proposedis to allow the subscribers instruments to remain of the manual type andto provide automatic switching equipment in the various outlyingexchanges which is controlled on a semi-automatic basis by an operatorat the parent main exchange, the equipment in response to a signal froma calling subscriber being adapted automatically to connect such partywith the main exchange operator.

1 With such arrangements every type of call involving a small exchangeof the network will require the intervention of the operator and thisnecessitates complex circuit switching arrangements. Furtherdisadvantages which can be raised are slowness in operation, andrestriction of network layout.

This application is a division of the application Serial No. 5829M),filed November 11, 1944, now Patent No. 2,508,635, issued May 23, 1950.

The chief object of the present invention is to provide an improvedtelephone system suitable for rural conditions which is far simpler andmore direct than semi-automatic exchange working of the type mentionedabove and which will operate over any subscribers line which is goodenough to enable manual signalling to be performed, i. e., good enoughto enable a relay at an exchange to be operated or released.

According to one feature of the invention use is made of the automaticselecting-principle disclosed in the Patent No. 2,421,169, issued May27, 1947, to Reginald Taylor and George Thomas Baker, which does notnecessitate reception of dialled impulses or the like from a callingpoint, the selection of any one or" a number of lines being initiated inresponse to a signal from a calling point, and proceeding untilterminated by a further signal from the calling point when the desiredline is encountered, the progress of the selecting operation beingindicated continuously at the calling point, for instance audibly.Preferably, each step of an exchange selecting switch will be indicatedto a calling party by means of a tone pulse applied to his line at theexchange.

This principle is employed in the various outlying exchanges of therural telephone network and its use enables local calls to be set upwithout the intervention of the main exchange operator thus relievingthe latter of a great deal of work, economizing in junctions andrendering the local exchange more independent of outside conditions. Alocal call can thus be made even if the outgoing junction is out oforder or engaged on another call. Where manual type subscriberstelephone instruments are already fitted, the modifications required tothe instruments are extremely small and chiefly involve the addition ofa controlling push button on or in association with each instrument.

For local calls a calling subscriber will remove his receiver and willdepress his push button to initiam the operation of a selecting switchat the local exchange. When the requisite number of steps have been madeby the switch as indicated by the number of tone pulses received, theoperation of the switch will be terminated by releasing the push button.Similar remarks apply if a second digit has to be signalled, any huntingor automatic stepping of the switch, which has to be performed after theinitial positioning operation taking place before the second controlledselecting and corresponding tone signalling operation is performed. Thecalling party thus gains access to a required line and subsequentlyafter the conversation is completed the connection is cleared when thesubscriber hangs up.

For calls outside the local exchange a calling subscriber will signal apredetermined digit, preferably greater than any required for localservice, whereupon a signal characterizing Out Service is automaticallypassed forward from the local exchange through to the operator at theparent main exchange, the signal being automatically repeated at anytandem exchange which may lie between the local exchange and the mainexchange. The wanted Out Service number is then given by the callingsubscriber to the operator and if this is for a subscriber on anexchange on the originating route, the operator will insert her callingplug into a jack associated with the incoming line and willprogressively dial back to set up the connection to the wanted party.When the operator has reached the wanted subscriber, a signal is passedforward from her position to connect together the calling and calledsubscribers and the operator can then listen in on the connection todetermine that it is proceeding satisfactorily. When she clears out ofthe connection, the route as far as the junction point is cleared downand the release of the established connection is then under control ofthe subscribers in conversation.

With the circuit arrangements according to the present invention thefacility whereby the operator can dial back over the originating route,although in itself not new, can be carried out in a much morestraightforward manner as will be evidenced from the ensuing descriptionfrom which other features of novelty will also appear.

The invention will be better understood from the following descriptionof one method of carrying it into effect, reference being had to theaccompanying drawings comprising Figs. 1-18.

Of these, Fig. 1 shows the layout of a typical rural telephone network,Fig. 2 shows diagrammatically atypical switching so eme for one arm ofthe network of Fig. 1, and Fig. 3 shows typical trunking arrangements ata tandem exchange, such as RE in'Fig. 1.

Fig. 4 shows a line circuit for a terminal or tandem exchange subscriberequipped with a magneto telephone instrument.

Figs. 5 and 6 when arranged side by side together show the circuit ofthe common equipment required for each of the automatic terminal ortandem exchanges of the network, this equipment serving to allot for usethe various local finder-connector l'nk circuits with which each suchexchange equipment is provided and to generate ringing and'other tonesas well as timing pulses.

Figs. '7 and 8 when arranged side by side together show the details of afinder-connector link circuit of an automatic exchange capable ofaccommodating nine subscribers and one junction line, an exchange ofthis size being employed only as a terminal exchange.

Figs. 9 and is when arranged side by side together show the circuit ofthe incoming selector of a terminal exchange.

Figs. 11 and 12 when arranged side by side together show the circuit ofa finder/ connector link of an automatic exchange capable of providingfor forty-two subscribers and seven junction lines, such exchange beingcapable of use either as a terminal or tandem exchange and having P. B.X hunting facilities.

Figs. 13, i4 and 15 when arranged side by side together show the circuitof an incoming selector of a tandem exchange, while Figs. 16, 17 and 18when arranged side by side show the circuit of a repeater of a tandemexchange.

The parent main exchange is assumed to be manual but it could or" courseoperate on a normal automatic basis as far as local calls are concerned,all calls into the rural network being handled via an operator at thisexchange.

Considering now the basis of operation of the system, although itstechnical functioning is novel, the main exchange operator need not beaware of this and will adopt the same procedure for setting up a call asfor normal semi-automatic exchange working.

As previously mentioned, all local calls are set up automatically by thecalling rural subscriber. All Out Service inter-exchange calls are setup under control of the main exchange operator, such calls beingvirtually independent of the local switching parts of the ruralexchanges so that it is justifiable to consider the system as involvingtwo quite distinct principles.

(a) Operator-controlled automatic dialling with reversion when required.

(o) Rural automatic exchange operation without dials at the individualstations.

In other words the rural exchanges may be visualized as independentunits tapping in to an operator-controlled connecting network. The twoportions will now be described independently, consideration first beinggiven to the connecting network.

Referring first to Fig. 1, the parent main exchange is designated P andconnects with a main exchange network over lines such as Ill. Tandemexchanges in one arm of the rural network are designated and RD, whilethe terminal exchanges are designated RA, RB and RC.

Considering now a call incoming to the rural network from exchange P andreferring to Figs. 1 and 2, each junction incoming to a rural exchangeterminates on an incoming selector to the banks of which are connectedthe local subscribers lines and also all outgoing junction lines. In thecase of tandem exchanges the incoming selectors are of the two-magnetvertical and rotary type with so-called rectangular release while in thecase or" terminal exchanges uniselectors are employed as incomingselectors. In general, levels 1-6, or their equivalent on uniselectorincoming selector banks, are allocated to subscriber and 70 to outgoingjunctions. In the tandem exchanges two-digit numbers in the series 11-60are allocated to the local subscribers while in the terminal exchangessingle digit numbers 1-0 are employed.

Hence considering Fig. 2, by plugging into the jack 0/ G correspondingto the outgoing branch the operator is connected to the incomingselector at rural tandem exchange RE. By dialling one of the digits 1-6followed by a second digit, the operator is connected to a subscriber onexchange If 8 or 9 is dialled, the selector is caused to hunt for andseize a junction to exchange RD or RA respectively. These junctionsagain terminate on incoming selectors which can be dialled on to any ofthe subscribers on the exchange concerned, or in the case of exchangeRD, 9 or 8 can be dialled giving access to exchange R3 or RC. Hence thistype of call involves plugging in and dialling the subscribers number ina straightforward manner.

With regard to calls from a rural subscriber to the operator, to anotherbranch of the network, or to an exchange outside the network, the digit'7 which is allocated to the operator is employed in all cases, and whenthis is signalled in accordance with the automatic selective principlementioned previously, the call is immediatel routed to the parent manualexchange P. For example, consider exchange RC, when 7 is sent, a relay0G therein is operated and the junction to exchange RD is seized. Inthis exchange a relay 0G is operated and a junction to RE is taken. Thisoperation is repeated automatically at RE and a calling signal is givenadjacent the answering jack I/ C at the parent exchange. If the operatoron inserting an answering plug ascertains that the call is for anotherbranch of the network, she inserts the calling plug into the appropriateoutgoing jack and dials the number in the same manner as for theincoming call already described. If the call is outgoing from thenetwork, it is extended over a line such as l 0, Fig. 1, in usualmanner.

